1. Field of the Invention
The present invention relates generally to a key input processing circuit for processing key input data from a key matrix circuit and for transmitting the processed data to a controller, such as a microcomputer, and more particularly to a key input processing circuit wherein a remote control signal can be incorporated and transmitted to the controller.
2. Description of the Prior Art
As shown in FIG. 1, a conventional key input processing circuit 1 comprises one LSI, to which a key matrix circuit 2 is directly connected, as well as a microcomputer 3, which is connected to the LSI via a number of serial communication lines 4. The microcomputer 3 serves as a controller for the key matrix circuit 2.
For reception of a remote control signal, a separately provided remote control receiving module 6 receives the remote control signal from a remote control transmitter 5, whereupon an encoded signal is extracted by removing a carrier wave from the received remote control signal, and then transmitted to the microcomputer 3 via a remote control transmission line 7, which is provided independently of the serial communication lines 4 for key data transmission.
The microcomputer 3 receives the encoded signal transmitted via the transmission line 7 at its interrupt terminal INT, and processes the encoded signal through an interrupt handling procedure.
Since the LSI, which constitutes the key input processing circuit 1, also incorporates a display driver, by inputting display data from the microcomputer 3 via one of the transmission lines 4 to the LSI (that is, a key input processing circuit 1), it is possible to drive a connected display 8.
As described above, conventionally, a communication line for transmitting key input data from the key matrix circuit 2 to the microcomputer 3 and a transmission line for transmitting the encoded signal from a remote-controller to the microcomputer 3 are different. Therefore, the conventional processing circuit has a problem in that the number of connecting lines between the circuit and the microcomputer are inevitably increased in order to allow incorporation of a remote control signal.
In particular, in a case of a stereo for use in a vehicle, since the key input processing circuit 1 and the remote control receiving module 6 are mounted on a front panel circuit board, while the microcomputer 3 is mounted on the main circuit board of the stereo, the number of connecters for connecting the connecting lines is also increased, as the number of connecting lines increases.
Moreover, as it may additionally control a CD player, a CD changer, a logic deck and so forth, as well as carrying out bus communication with external components, the microcomputer 3 is likely to be made unable to execute interrupt handling with respect to a remote control signal which has been input without prior notice, and therefore its function of receiving remote control data is impaired.